1. Field of the Invention
The invention relates to an elastomer bearing with hydraulic damping including a housing, a connecting element, an elastomer body which couples the housing and the connecting element with one another for damping oscillations, two chambers filled with a magneto-rheological fluid, a flow channel which connects the chambers with one another for fluid conduction, an actuator associated with the flow channel and mounted on the outside of the housing for generating a magnetic field.
2. Description of the Related Art
With increasing desire for comfort, damping of vibrations generated internally in an automobile and/or of externally introduced vibrations, which are transmitted for example from the road surface to the vehicle, becomes more and more of an issue. This is particularly important for reducing the noise level in the vehicle interior and reducing vibrations perceived as annoying. Elastomer bearings are used increasingly because of the advantageous resilient and damping properties of materials, for example for supporting the engine or moving parts in the automobile. The specific geometry and the composition of the elastomer has a major impact on the quality and the damping properties. The firmness and elasticity of the elastomer bearing can thus be significantly affected by changing the material composition of the elastomer. However, this variability has limits where large vibration amplitudes have to be damped. These are produced, for example, when the engine is idling or when a periodic or impulse motion is transferred to the chassis on an uneven road surface. In these situations, elastomer bearings with hydraulic damping are increasingly employed in automobiles.
These elastomer bearings have at least two mutually independent chambers containing a damping fluid. The chambers are connected with one another via a flow channel and are deformed by an external force applied to the elastomer bearing, so that damping fluid can flow from one chamber into the other.
The chamber walls resist the change in the shape, and the resistance causes a pressure change in the chambers. A measure for this pressure change caused by the produced volume displacement is referred to as “buckling spring rate.” To equalize the pressure difference between the chambers, the chambers are connected via the aforementioned flow channel. During spring deflection at low frequencies, the pressure between the chambers is equalized exclusively via the flow channel. The elastomer body hereby significantly contributes to the spring characteristic and the damping characteristic of the elastomer bearing. However, a damped system capable of performing oscillations becomes more and more important at higher frequencies, wherein the damped system consists of the elastic chamber walls and the mass of the damping fluid located in the flow channel. The various contributions to the total damping effect of the elastomer bearing are, on one hand, the internal friction of the damping fluid in the channel and, on the other hand, the losses from the dynamic pressure.
When an elastomer bearing with hydraulic damping is excited in the range of a resonance frequency, the damping changes, which causes the overall elastic characteristic of the elastomer bearing to change. Above the resonance frequency, the inertia of the fluid quantity in the flow channel and the friction prevent a further pressure equalization between the chambers. The stiffness of the chamber walls then supports the stiffness of the mount and causes an increase in the total stiffness compared to the low-frequency load condition.
A hydraulically damped elastomer bearing composed of a housing and a connecting element is known from DE 103 29 982 B4. The housing and connecting element are coupled with one another via an elastomer body to dampen vibrations. The elastomer bearing also has two chambers filled with a magneto-rheological fluid. These chambers are connected with one another for fluid conduction via a flow channel. An actuator mounted on the outside of the housing is associated with the flow channel, with the actuator generating a magnetic field that is applied to the magneto-rheological fluid. The actuator is an electromagnet which generates an electromagnetic field with curved field lines extending between the poles. The field strength decreases with the distance from the electromagnet, so that with conventional solution is incapable of producing a uniform change of the properties of the magneto-rheological fluid inside the flow channel.